The present invention relates to means for adjusting camera electric circuits, and more particularly, to means for adjusting camera exposure control circuits.
In the past, a method for adjusting camera exposure control circuits or a method for adjusting a camera exposure level, a display level and the like, has been mainly by employing a semifixed resistor (trimmer resistor) or by adjusting an analog quantity with the trimming of a fixed resistor (employing a laser and the like).
An example of such a conventional adjusting means will be described with reference to FIG. 8. A photographing operation with an automatic exposure for a single-lens reflex camera is as follows. Information on brightness of an object being photographed is introduced through a photographing optical system or the like (not shown) into a photometric element 1 and is converted into a photocurrent therein. The photocurrent is further converted into a logarithmically compressed voltage by a photometric circuit comprising an operational amplifier 2 and a compression diode 3. The voltage is compensated in temperature and is adjusted in level by a diode 4 for compensating temperature, a semifixed resistor 5 for adjusting a level and a constant current source 8 and is then fed through an analog multiplexer 9 into an A/D converter 10. An aperture information voltage from a resistor 6 and a film sensitivity information voltage from a resistor 7 are fed through the multiplexer 9 into the A/D converter 10 to be subjected to an A/D conversion. An output from the A/D converter 10 is fed into a calculator 11. The calculator 11 digitally calculates a shutter speed Tv (denoted by the APEX system) for a proper exposure using the following well known equation: EQU Tv=Sv+Bv-Av
of the APEX system; where Av is an aperture value, Bv is a brightness value of an object being photographed and Sv is a film sensitivity value. Then, when a release initiate means (not shown) starts to stop down, the calculator 11 counts pulses from a contact piece 12 which slides in cooperation with the stop down operation. When a given number of pulses is reached, the calculator 11 turns a switching element 13 on to allow a magnet 16 for locking an aperture to operate, thereby terminating the stop down operation. Subsequently, upon rise of a movable mirror, a switching element 14 is rendered on to operate a magnet 17 for running a first shutter blind, thereby the first blind starts to run. After a time period calculated above, a switching element 15 is rendered on to operate a magnet 18 for running a second shutter blind, thereby the second blind being released to start running. Thus, the photographing operation is completed.
In the above photographing operation with automatic exposure, values of transmittivity of an optical system in a camera, efficiency of a photosensitive element, current of the constant current source 8, and resistances for setting a film sensitivity and an aperture vary, so that, after an A/D conversion of the values, these converted digital data are: EQU Bv'=Bv+.DELTA.Bv, EQU Av'=Av+.DELTA.Av, and EQU Sv'=Sv+.DELTA.Sv,
including errors .DELTA.Bv, .DELTA.Av and .DELTA.Sv.
To eliminate these errors, a conventional method compensates them by interposing the semifixed resistor 5. Specifically, the Bv value is corrected by a compensation value .DELTA.Cv and the corrected Bv value is subjected to an A/D conversion. While performing an assembling process, under the condition that a given amount of light is given to a camera, an exposure level is inspected and its deviation from a proper exposure value is compensated by adjusting the semifixed resistor 5. In other words, the calculator 11 actually calculates: EQU Tv=Sv+.DELTA.Sv+Bv+.DELTA.Bv-.DELTA.Cv-(Av+.DELTA.Av),
adjusting .DELTA.Cv so as to obtain the relation: EQU .DELTA.Cv=.DELTA.Sv+.DELTA.Bv-.DELTA.Av.
In the conventional method of adjusting a semifixed resistor, however, an assembler or inspector reads an output from a circuit by an indicator and adjusts a semifixed resistor to a desired value, so that it is time-consuming, and it is difficult to reduce the cost of parts and assembling and also to automate the adjustment. Although a trimming with a laser or the like can be automated, there are such problems that an apparatus for the trimming becomes a large scale undertaking and readjustment is impossible; specifically it is practicable while electric parts are assembled on a substrate but it is impracticable while they are assembled in a case body of a camera.
Lately an EEPROM (electrically erasable and programmable read only memory) of a small capacity has been developed as a non-volatile digital memory element. The EEPROM is introduced under the item "aiming at a cost reduction by integrating an EEPROM on an analog-digital hybrid CMOS custom IC" in Japanese magazine "Nikkei Electronics", July 1, 1985, page 235, in which it has remarkable effects on an economical advantage because of integrating only a required capacity and a DIP (dual in-line package) switch is replaceable by it. Thus, the EEPROM is suitable for storing operational procedures of instruments or the like and for calibration thereof. Also, it is possible to store and to renew a program. In addition, it is possible to use for trimming an analog circuit. As such, the range of its use is increasing from a digital circuit to an analog circuit.